Italian Cheese
MILK DOES NOT COAGULATE
Your milk may be old or perhaps it is pasteurized beyond usefulness. Your rennet may also be unviable or old. Try changing milks and if the problem persists, buy new rennet.
MILK COAGULATES TOO FAST
The milk you are using may be too acidic. This can be caused by too much culture addition or an overly long ripening period. You can fix this by using less starter next time or try shortening the ripening time.